If its a good review, should not be a problem posting it anywhere in many cases.
However, posting a bad review could get you some LSD, and I don't mean the crazy, far out 1970s trip drug either!
I mean Libel, Slander, Defamation law suits.
You write it....you post it....you own it....
Curious though, without naming the realtor, what did they do that was so great or so bad?